1. Technical Field
The current invention relates generally to the production of nitride based heterostructure devices. In particular, the present invention generally relates to nitride based heterostructures having a quaternary barrier layer that comprises AlInGaN for controlling strain, band offsets and lattice mismatches in the devices.
2. Background Art
The large lattice mismatch between GaN, AlN and InN and the strong piezoelectric and polarization effects in these materials significantly impact the electrical and optical properties of III-N heterojunction devices. Nearly all the reported GaN-based High Electron Mobility Transistors (HEMTs) to date use strained GaNxe2x80x94AlGaN junctions with alloy compositions below 35% and 15-20 nm thick barriers to avoid exceeding the critical thickness for the development of dislocations relieving strain. Such strain produces piezoelectric doping with about 1xc3x971013 cmxe2x88x922 sheet carriers. Additionally, the strain may be responsible for the long-term instabilities observed in some AlGaN/GaN HEMTs.
Therefore, there exists a need for a method and system of building heterojunction devices so that lattice mismatch, and consequently strain, is controlled. As a result, the heterojunction device can be designed to take advantage of piezoelectric and spontaneous polarization effects and long-term instabilities can be minimized.
The current invention provides a method and system of independently controlling strain and band offsets by providing nitride based heterostructures having a quaternary layer that comprises AlInGaN (Aluminum Indium Gallium Nitride).
The current invention employs strain engineering to demonstrate the influence of piezoelectric and polarization effects in AlInGaN/GaN heterostructures having different indium content. The obtained results show that the contribution to two-dimensional electron gas from spontaneous polarization is approximately equal to the piezoelectric charge. The piezoelectric doping not only changes the sheet electron density but also strongly affects the transport properties of two-dimensional electron gas. The obtained results show that in AlGaN/GaN heterostructures with 12% aluminum, the piezoelectric effects increase the sheet density-mobility product, nsxcexc, at room temperature by a factor of 5. Under the present invention, a low pressure Metal Organic Chemical Vapor Deposition (MOCVD) can grow, for example, AlxInyGa1xe2x88x92xxe2x88x92yNxe2x80x94GaN heterojunctions over sapphire, 6H/4H SiC and other substrates, such as silicon or spinel.
In a first aspect of the present invention, a method of producing nitride based heterostructure devices is provided comprising the steps of providing a substrate; and applying a quaternary layer over the substrate, wherein the quaternary layer comprises In.
In a second aspect of the present invention, a method of producing nitride based heterostructure devices is provided comprising the steps of: providing a substrate; applying a first layer comprising GaN over the substrate; applying a ternary layer over the first layer, wherein the ternary layer comprises a compound selected from the group consisting of AlGaN and InGaN; and applying a quaternary layer over the ternary layer, wherein the quaternary layer comprises AlInGaN.
In a third aspect of the present invention, a nitride based heterostructure device is provided comprising: a substrate; a first layer applied over the substrate; and a quaternary layer applied over the first layer wherein the quaternary layer comprises In.
In all these aspects, the Al and In composition might vary between the layer thickness in order to optimize the starin distribution and the band offsets.
The exemplary aspects of the present invention are designed to solve the problems herein described and other problems not discussed, which are discoverable by a skilled artisan.